I'm driving my project pickup 1978 3/4 ton 2wd that I put on a 1979 3/4 ton 4wd frame and running gear. Both have 4.10 gears, 2wd had 31x10.5x16.5 tires and the 4wd has 235/85/16, both have c6 trannys but my speedometer is off about 10 mph at 60 (it reads 70) do I need a new gear on my speedometer cable since it's a 4wd now? I wouldn't think so but not sure...I'm using the 2wd speedometer cable and gear on the 4wd tranny. Ideas? Thanks.

 

You will need to change out the gear on the speedometer cable, the one that slips into the transmission, or transfer case.
Since the speedo is reading too fast you will need to install a gear with more teeth. I would start with a gear with two more teeth than your current gear.

Be aware there are left handed and right handed gears. Be sure your replacement gear is the same cut as the original.

Good luck.

 

For your shopping pleasure.
Ford stuff is down the page a bit.
Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4

 

Ok I'll switch it out...thanks guys.